The present invention relates to an absolute position detector for detecting the absolute position of a rotation shaft.
Conventionally, an absolute position detector including reduction gearing and a plurality of resolvers is miniaturized by installing the resolvers on an input shaft.
FIG. 1A is an axial cross section view showing an embodiment of an absolute position detector proposed by the same applicant. FIG. 1B is a cross section view taken along line I--I of FIG. 1A.
As shown in FIG. 1A, the input shaft 1 of the absolute position detector is installed through bearings 63, 64 which are housed a casing 61 of a flange 60. A gear 10 is fitted to the input shaft 1. A reduction gear system is provided in such a manner that the rotation of a gear 11 engaged with the gear 10 causes a gear 12 fitted to a shaft 2 of a gear 11 to rotate. The rotation of a gear 13 engaged with the gear 12 causes gears 14 and 15, both being fitted to a shaft 3b of the gear 13, to rotate. The rotation of the gear 13 further causes gears 16b and 17b, respectively engaged with the gears 14 and 15, to rotate. By this reduction gear system, a cylindrical output shaft 4 fitted to the gear 16b rotates one turn for every twenty four rotations of the input shaft 1, while a cylindrical output shaft 5 fitted to the gear 17b rotates one turn for every twenty five rotations of the input shaft 1.
A rotor 73 is attached to the input shaft 1 with the aid of a key 76 and a rotor 74 is attached to the output shaft 4 with the aid of a key 77b. Further, a rotor 75 is attached to the output shaft 5 with the aid of a key 78b. Stators 70, 71, 72 corresponding to the rotors 73, 74 75 are fixed to the casing 61. The stators 70, 71, 72 and the rotors 73, 74, 75 are made of a magnetic material. The rotors 73, 74, 75 are cylindrically shaped and are attached to the shafts 1, 4, 5 respectively so as to revolve eccentrically relative to the rotation centers of the shafts 1, 4, 5. Each of the stators 70, 71, 72 has four pole teeth and primary windings 84, 85, 86 for providing exciting pulses are wound around the four pole teeth of the respective stator. If the three pole teeth arranged in the axial directions of the stators 70, 71 72 are regarded as one set of pole teeth, secondary windings 80, 81, 82, 83 for outputting amplitude modulation waves are wound around four sets of the pole teeth respectively. Two sets of the secondary windings 80, 82 and 81, 83 are connected in series to each other. By this arrangement, when one of the primary windings 84, 85, 86 is pulse-excited, a pulse voltage is output from the both edges of two sets of the secondary windings 80, 82 and 81, 83 by a reluctance difference between a rotor in response to a excited stator and the four excited pole teeth. The pulse voltage is amplitude-modulated to sine and cosine values of a rotor rotation angle corresponding to an excited stator.
FIG. 2 is a block diagram showing the absolute position detector shown in FIG. 1 and an embodiment of its encoding circuit. The components in FIG. 2 which are the same as those in FIG. 1 are denoted by the same reference characters and the explanations thereof are omitted. Resolvers 20, 21, 22 in FIG. 2 respectively correspond to resolvers which are made up of the stator 70 and the rotor 73 the stator 71 and the rotor 74 and the stator 72 and the rotor 75 shown in FIG. 1.
Pulse excitation signal generators 30, 31, 32 sequentially pulse-excite the primary windings 84, 85, 86 of resolvers 20, 21, 22 according to pulse excitation signals P.sub.ex0 P.sub.ex1, P.sub.ex2 based pulse excitation signals Pex 0, Pex 1, Pex 2 based on timing signals P.sub.0, P.sub.1, P.sub.2 from a timing controller 42. For this reason, pulse signals S, C are sequentially outputted to the secondary windings 80, 82 and 81, 83 for outputting the amplitude modulation signal, the secondary windings 80, 82 and 81, 83 being shared by the resolvers 20, 21, 22. The pulse signals S, C are amplitude-modulated to the sine and cosine values of the rotor rotation angle of the excited resolver and are further inputted to A/D converters 40, 41. The A/D converters 40, 41 convert two types of pulse signals S and C by a conversion start signal C.sub.start from the timing controller 42 into numerical values and output the pulse signals as sine signal D.sub.s and cosine signal D.sub.c. The sine signal D.sub.s and the cosine signal D.sub.c outputted from the A/D converters are inputted to a microcomputer 50. Timing signal t.sub.1 from the timing controller 42 allows the microcomputer 50 to determine which resolver the signals come from. Furthermore, the microcomputer 50 computes the following equation (1). However, since the rotation direction of the rotors of the resolvers 21, 22 is opposite to that of the input shaft 1, the microcomputer 50 computes equation (1) after the sine signal D.sub.s and the cosine signal D.sub.c are converted to determine rotor rotation angles .theta..sub.21, .theta..sub.22. ##EQU1##
By the above-described process, data .theta..sub.20, .theta..sub.21, .theta..sub.22, corresponding to the rotor rotation angles of the resolvers 20, 21, 22, is obtained. The microcomputer 50 further computes the following equation (2) to determine .theta.'. EQU .theta.'=.theta..sub.20 +256.times.((24.times..theta..sub.21 -.theta..sub.20 +128)/256) (2)
The above equation (2) is computed using only integers.
As shown in FIG. 3, the determined .theta.' can be represented by any number from 0 to 6143, and denotes the rotation angle of twenty four rotations of the input shaft 1.
The microcomputer 50 then computes the following equation (3) to determine .theta.". ##EQU2##
The above equation (3) is computed using only integers.
As shown in FIG. 4, the determined .theta." can be represented by any number from 0 to 153,599, and denotes the rotation angle of six hundred rotations of the input shaft 1. If necessary, reference is made to Japanese Patent Application No. 63-163049.
Such a conventional absolute position detector as described above requires much space among the rotors of the resolvers in order to avoid magnetic interference between the adjacent resolvers. Furthermore, concentrically circular cylindrically output shafts are required for each rotor, because the rotor rotation ratios with respect to the input shaft of the resolvers arranged on the same axis are different. Therefore, the conventional absolute position detector has a disadvantage in that it is large.